The present invention relates to electric equipment used for automatic monitor and control purposes and in particular, to a thermal bimetallic strip relay.
The thermal bimetallic strip relay is intended to enable and to disable an electric network whenever the ambient temperature of the medium under control deviates from the present value.
The prior art knows a thermal bimetallic strip relay comprising a sensor made as a thermal bimetallic "clapping" disk, moving and fixed contacts located inside a case with a lid which is provided with external leads and a device for eliminating the analog (smooth) run of the "clapping" disk.
Such a relay suffers from a drawback which consists in that the sag of the "clapping" disk varies in the course of operation and the relay tends to open the contacts before the disk could alter its state with a clap. Hence, the process of contact opening becomes smooth, which leads to contact burning and reduces the commutability of the relay.
Known in the art also is a more advanced thermal bimetallic strip relay which comprises a metal case, a lid having fixed contacts provided with external leads and secured to its internal surface, a "clapping" thermal bimetallic sensitive element having moving contacts arranged opposite the fixed ones, an upper and a lower supports rigidly mounted inside the case so that the center of the clapping sensor is located between them.
The sag of the "clapping" disk in this relay also changes, due to which the contacts open in a smooth way either before or after the sensor clap. Hence, the contacts suffer from excessive burning.
The normal operation of the relay can be provided by means of straightening the "clapping" sensor so that its sag remains constant and would not open the contacts when heated before its temperature reaches the clap level, i.e. below the operation temperature.
The required straightening can be obtained by machining relay parts to high precision. The precise dimensions are as follows: the height from lid to case bottom, height of the fixed contacts, height of the rigid upper support, height of the rigid lower support, thickness of "clapping" sensor. However, this requirement leads to considerable complexity of the relay design.